Radio signaling system



Patented July 14, 1931 1 .-)UNITEDYM sra'ras Rossum.y sfoHLjoF NEW YORK, N. Y., assIGNoR To AMERICAN TELEPHONE YAND.

Tnnncanrn COMPANY, n CORPORATION oFMNnw Yom; Y

\ RADIOv srGNALINa SYSTEM Application filed August 26, 1925. SeralvNo. 52,552. i

This invention relates to signaling systems, and particularly to multiplex signaling systems employing piezoelectric oscillators.

An object of the invention is to provide a plurality of signaling channels in the small range of the frequencyspectrum. f

^ Another object kof the invention is to employ a plurality .of piezo-electric oscillators to obtain amaXimum number of signaling channels within' va given frequency band.

A further object is tol provide a. signaling system in which carrier waves are locally supplied-to the transmitting and receiving ends of such a signaling system sothat the carrier waves will `be at thesame frequency or at the same frequency difference, as conditions necessitate.V

`This invention is applicable to signaling systems generally, and is illustrated as a radio signaling system wherein a plurality of messages may be transmitted from a single antenna or over a wire line and receivedby a Y plurality of receiving stations connected to a receiving antenna or a common wire line. It will be understood, however, that separate antennae may be applied at either transmit,- ting or receiving stations without impairing in any way the effectiveness of the invention.

The carrier waves employed in this invention are supplied to the various circuits of the system by means of one or more oscillaf tion generators.

A generators employed in this invention are of the carrier waves.

ihe type known as piezo-electric oscillation generators, and such oscillation generators vibrate at frequencies which are substantial-- ly constant within narrow limits. By providing piezo-electric oscillation generators it is possible to reduce the allowance necessarily made inthe frequency spacing between carrier waves of different signaling channels for variations in the frequency of Consequently, itis possible to materially increase the. number of channels employed in any given frequency range `and Ystill avoid interference bet-Ween channels. Stated conversely, the band of the frequency spectrum required for transmitting a given rnumber vof signaling chan- Some of the oscillation whichfa transmitting'station is designated* by the reference character A, and a receiving station is designated by the reference character B. `At the transmitting station A there are a plurality of transmitting channels, T121, TL2, TL3 and TLr, and a plurality of piezo-electric oscillatorsv represented by the reference ycharacters HFI, HF2, HF3 and HF4. .For the purpose of illustration, let it be.A assumed `that the piezo-electric oscillators employedat the transmittingy station A vi-L brate atfrequencies of 10,000, 10,001,10,002 and 10,003 lilocycles, respectively. It will be understood that-these oscillators'may be any oscillators capable of 'setting up oscillations which are constant in frequency within very narrowlimits, sothat a plurality of suchoscillators may be closely spaced and all arranged in a. small band of the frequency spectrum. y

A plurality of low frequency signaling channels, L1, L2, L3 and Laga-re connected to Vcorresponding low frequency signaling sources. The low frequency signaling channels Ll, L2, La and *L4 transmit currents which may have frequencies of 1,2, 3 and 4' kilocycles, respectively, and each operates a signaling relay such as SR1, SR2, SR3 and S114. When currents of 1, 2, 3and 4; kilocycles flow through Lthe respective channels L1, L2, L'and L4 the corresponding relays SR1, SR2, SR2, and SR4, which are of any well known type -readilyfresponsive to valternating current of definite'y frequency, become energized. It will'be understood, however, that if the vchannels L1, L2, L3 and L4 are employed merely to transmit direct current pulses characteristic of telegraph signals,

Vspect to the signaling channels that the currents of the signaling channels are amplified thereby. This amplifier A1 may be' of any type well known in the art, but is preferably a' vacuum tube amplifier'. The input circuit of amplifier A,L consists of the grid and .cathg ode of the amplifier A1,'the inductance z', re-

sistance r, and the' winding ofthe electromagnetic relay m. The anode of the vacuum tube A1 is supplied with space current by means of a source of' potential p. W'hen the input circuit of the amplifier A1 is energized, direct current flows through the winding of the electromagnetic relay m, energizing said relay and attracting the armature a. By virtue of a grounded connection of the armaturea, the source of potential 29 is connected to the anode of the amplifier A1. However, when no current is impressed on the input circuit of the vacuum tube A1v the winding of the electromagnetic relay m is deenergized andv the armature a is released so thatk the source of potential p isV disconnected from the output circuit of the amplifier A1. The adjustable condensers c1V and 02 are respectively connected in the input and output circuits of the amplifier A1 to prevent any stray orv harmonic frequencies from being impressed on the circuits. The modulated carrier currents, as amplified by amplifier A1, are impressed on the antenna at station A and are then transmitted to an antenna of station B.

A t station B there is another piezo-electric oscillator O1 which vibrates at a frequency, for example, 10,049 kilocycles, which is'different from the Jfrequencies of the piezo electric oscillators HFl, HFZ, HFS and HF? The modulated carrier currents transmitted by the apparatus at station Av are impressed on the input circuit of a detector D1. The oscillations of the`piezoelectric oscillator O1 are impressed onthe input circuit of the modulator M. The anodes of the detector Dl and the modulator M are tied together so as to permit the oscillations ofthe piezo-electric oscillator Ol to vbeat with the oscillations of the modulated carrier currents transmit'- ted by the apparatus at stationV A. A filter andint'ermedia'te frequency amplifier A2 is connected to t-he output circuits of the del tector D1. andthe modulator M, the filter functioning to suppress all frequencies except the band of frequencies represented by the difference between the frequency of the oscillator' O1 and the modulated carrier frequencies transmitted by station A. Thus a band of intermediate frequencies of the order of 46, 47, i8 and 49 kilocycles, which are modulated in accordance with low frequency signals, is amplied by the amplifier A2. It will lbe' understood that the amplifier A2 may be of any type well known in the art, preferably a vacuum tube amplifier.

Another oscillation generator O2 is employed for beating with the band of intermediate frequencies. The frequency of this oscillation generator is different from rthe frequencies of the intermediate band, for example, lilocycles.Y It willbe understood that this oscillation generatormay be of any well known type, preferably a vacuum tube oscillator. A detector D2 is arranged so that the oscillations of theoscillator O2 and the bandv of intermediate frequencies are beatenY therein so as to reproduce the origin-al signaling currents. A plurality offilters, for example, LFI, LFZ, LF3 and LF, are serially arranged with respect to the output'xcircuit of the detector D2, each freely'transmi'tting. the current of the corresponding low frequency signal transmitted fromfsta-tionA. Thus the filter LF1 will transmit the signals impressed onthe channel L1 of station A totheV channel L1 at station B; filter LFL will transmit the signals impressed on the channel L2 of station A to the channel L2 at station B; the filter LFS will transmit the signals impressed on the channel L3 of station A tothe channel Iig/,at station B and the filter LF.1t will transmit the signals impressed on the channel L4 of station A to the channel L4 at station B. It will be understood that thev filters employed herein are of any well known type,l preferably the type known as the Gampbel-l filters, described in Patent No. 1,221',1lf3 to' 'Gn A. Campbell, dated May 22, 1917.

The'arrangements of this invention oper4` ate in the following manner:v

A plurality of high frequency signaling. currents, all conveniently separated from4 one another and in a small range of the frequency' spectrum, are generated by the oscillators HFl, HF2, HFS and HEL. EachV of: these high frequency oscillations' is modulated in accordance with alow frequency signal, such as is found in channels L1, L2, L3 and L4. The high frequency carrier currents as thus modulated are impressed upon the common transmitting channel GL,. and are then transmitted to the input circuit of the amplier A1. After amplification by the amplifier Al the modulatedl high: frequency carrier currents are impressed upon the antenna andare then transmitted' to the distant station B.

. Thus, the modulated carrier currents transmitted by the apparatus at station A are irnpressed upon the antenna of `station B and thence upon the input circuit of the'detector D1. The oscillations of the piezo-electric oscillator O1 Which has a frequency different from the frequencies of the carrier currents transmitted by the apparatus at station A, are impressed on the input circuit of the modulator M. The oscillations of this oscillator O1 beat with the modulated carrier currents received from station A inthe plate circuits of the detector D1 and modulator M. Of

` the products of modulation a band of intermediate frequencies is selected and amplified by the amplifier A2. Another oscillator O2 sets up oscillations which beat With the band of the intermediate frequencies in the detector D2. The frequency of the oscillator O2 is different from the frequencies amplified by the amplifier A2. As a result of the beating of these frequencies the original signaling frequencies are reproduced, these being then selected by filters LFl, LITg, LF3 and LF4 into the corresponding channels L1', L2, L3 and L4', respectively. Y

It Will be understood that the'frequencies employed herein are merely illustrative and others may be substituted therefor in practice as conditions necessitate.l

' While the invention has been disclosed in one particular embodiment which is deemed desirable, it is to be understood that it is capable of embodiment in other and Widely varied organizations Without departing from the Vspirit and scope of the invention as deiined in the appended claim.

What is claimed is:

In a radio signaling system, in combination, a transmitting station including a plurality of oscillators connected in parallel relationship producing currents of different high frequencies Which are closely spaced, a plurality of piezo-electric devices one coupled to each oscillator and maintaining the frequency of its current constant Within very narrovrT limits, a plurality of relays one associated with each oscillator, the armature of each relay controlling the output of the corresponding oscillator, a plurality of lines one extending to the Winding of each relay, currents of different lovv frequencies being transmitter over said lines each interrupted in accordance With signals and means capacitatively coupled to said high frequency oscillators for transmitting the high frequency currents modulated in accordance With said signals, and a receiving station including means for receiving said high frequency currents modulated in accordance With said signals, a first oscillator producing current of a frequency different from those frequencies received by said receiving means, a piezoelectric device counled to said first oscillator for maintaining the frequency of the current produced thereby constant4 Within very narrupted in accordance with the same signals, i

a second oscillator, and means for beating the various currents of said intermediate frequencies interrupted in accordance with said signals and the current of said second oscillator in order to reproduce low frequency l, currents interrupted in accordance With said signals.

In testimony whereof, I have signed my name to this specification thisl 24th day of August, 1925.

RUSSELL S. OI-IL. 

